Descartes: Mind, Body, and Reality

Descartes' View of Mind and Body

Descartes' anthropology presents man as a composite of two distinct substances: res cogitans (the thinking substance or soul) and res extensa (the extended substance or body). These substances are considered independent and autonomous.

The Mind-Body Problem

Two important questions arise from this dualism: how do these substances relate, and how do they communicate? Their relationship is undeniable: when the soul gives orders, the body obeys. Descartes' duality of man is a direct result of his metaphysical dualism.

Since the understanding has a clear and distinct idea of thinking substance and a clear and distinct idea of extended substance, it is evident that these are two different, independent substances. This implies that the soul can exist without the body; that is, the death of the body does not necessarily lead to the death of the soul.

Other rationalists and philosophers inherited this problem of mind-body communication. Descartes's proposed solution is that the soul joins the body through the pineal gland (located in the brain). In this gland, soul and body interact in such a way that when the soul has a thought, it passes through the pineal gland, and when the body feels pain, it is communicated through the pineal gland.

This explanation involving the pineal gland was not satisfactory and has been disproven by science, though the mind-body problem itself remains a philosophical mystery and an inherited problem in philosophy.

Thinking Substance (Res Cogitans)

The res cogitans (thinking thing / mind/soul) is identified with the soul. The soul is considered immortal, one, and indivisible. Its essence is thinking, and it is equipped with several faculties such as internal and external senses, common sense, imagination, memory, intellect, and will, which are the most important and characteristic of the soul.

Extended Substance (Res Extensa)

The human body, or res extensa, is understood as a machine governed by the laws of mechanics, with the heart often seen as a key component. In this mechanical view, the soul is not the principle of life in the sense of vital force; life is reduced to mechanical movement. The life of the body is reduced to mechanical motion. Feelings, however, are considered modes of thought and thus belong to the soul.

The mechanism of the physical world, according to Descartes, can be summarized: God creates inert matter and injects into it a momentum that remains constant. The cause of movement and its conservation is God (related to the concept of the Law of Inertia).

Descartes' Metaphysics of Substance

Seventeenth-century philosophers, influenced by scholastic background, sought to understand reality and substance. Descartes posits three types of reality or substance: God (infinite substance), and finite substances (created by God), which include the world (extended substance) and human beings (composed of thinking and extended substance).

The Concept of Substance

Descartes retains and modifies the traditional concept of substance. For Descartes, substance has several features: it is a thing that exists in such a way that it needs no other thing in order to exist (strictly speaking, this applies only to God); it is a permanent and stable element of reality that supports accidents (attributes); and the idea of substance is innate. Modes are modifications or particular instances of a substance through its attributes.

Three Types of Substance

Descartes claims that substances are known through their principal attributes:

Infinite Substance (God)

Infinite Substance or God (res infinita) whose principal attribute is infinity, and whose modes are all possible perfections.

Finite Thinking Substance

Finite Thinking Substance, the self, the soul (res cogitans) whose principal attribute is thought, and whose modes are thinking, imagining, feeling, denying, doubting, affirming, etc.

Finite Extended Substance

Finite Extended Substance, things, the world (res extensa) whose principal attribute is extension (length, width, depth), and whose modes are size, shape, position, and movement.

Relationship Between Substances

The infinite substance is God. Res cogitans and res extensa are considered substances in a secondary sense because, while they depend on the infinite substance (God) for their creation and preservation, they do not depend on each other to exist.

The soul (res cogitans) is free, while the body (res extensa) is governed by the laws of physics (mechanism).

Subjectivity and God's Role

Descartes' system revolves around the self (the thinking subject), giving his metaphysics a subjective nature that would have great influence. God is not the primary focus as in the Middle Ages, but is necessary as a guarantee of our knowledge and the creator/preserver of finite substances.

Recall that the existence of the infinite substance (God) and extended substance (matter) is argued to follow from the existence of the thinking substance (the self).